Trapezionida aequispina, Tiwari & Padate & Cubelio, 2023

Tiwari, Shivam, Padate, Vinay P. & Cubelio, Sherine Sonia, 2023, Chirostyloid and galatheoid squat lobsters (Decapoda: Anomura) from Andaman and Nicobar Islands, India, with three new species, Journal of Natural History 57 (9 - 12), pp. 520-556 : 541-546

Trapezionida aequispina sp. nov.

( Figures 2 (e), 10, Supplementary Figure S3 )

Material examined

Holotype. Ovigerous female (7.0 mm PCL, 6.0 mm CW) (IO/SS/ANO/00137), Andaman Sea, off Car Nicobar Island, FORVSS stn 355II04, 9.31°N 92.82°E, 109 m depth, Naturalist ̍s dredge, coll. Vimal Kumar K. G., 12. January 2017.

Paratypes. 1 male (3.9 mm PCL, 3.5 mm CW) (IO/SS/ANO/00138), same data as holotype; 1 ovigerous female (6.6 mm PCL, 6.0 mm CW) (IO/SS/ANO/00139), Andaman Sea , off Car Nicobar Island, FORVSS stn 334II05, 9.24°N, 92.92°E, 315 m depth, Naturalist ̍s dredge, coll . Vinu Jacob, 28 January 2015.

Etymology

The species name is derived from two Latin terms ′ aequalis ̍ (adjective for ′equal̍) meaning equal-sized and ′ spina ̍ meaning spines, denoting the almost equal size of the distal spines of antennular peduncle article 1.

Diagnosis

Carapace with 6 pairs of epigastric spines and 2 median spines; hepatic, parahepatic, anterobranchial and postcervical regions each with 1 small spine; frontal margin transverse; anterolateral spine reaching sinus between rostrum and supraocular spines; branchial margins with 5 spines. Rostrum spiniform, 0.4 times as long as PCL, supraocular spines 0.4 times as long as rostrum. Pterygostomian flap with anterior margin terminating in 1 spinule. Thoracic sternite 4 with 2 pairs of oblique striae, anterior pair shorter, anterior margin widely contiguous to sternite 3. Sternites 5–7 each with 1 short stria anterolaterally, sternite 5 with 1 longitudinal stria midlaterally. Pleonal tergite 2 with 1–2 lateral spines on anterior ridge. Eye wider than sinus between rostrum and supraocular spine. Antennular peduncle article 1 bearing subequal distal spines. Distomesial spine of antennal peduncle article 1 reaching distal margin of article 3; distomesial spine of article 2 overreaching distal margin of article 4, mesial margin with short spine, distolateral spine not reaching distal margin of article 3; article 3 with minute distolateral spine. Mxp 3 merus with 3 flexor spines, extensor margin with distal spine. P1 length 2.7–3.1 times PCL, merus 4.1 times as long as wide, with 10 spines on dorsal surface, 3 spines on mesial margin, 2 rows of spines on ventral surface; palm 3.1 times as long as wide, dorsal surface with 2 rows of small spines, dorsomesial margin spinose; fingers subequal to palm length, fixed finger with 2 spines on dorsolateral surface, 2 subdistal spines on lateral margin, dactylus with short proximal spine, 2 subdistal spines on mesial margin, 2 spines on dorsomesial surface. P2–4 squamate with iridescent setae on margins; dactyli 0.7–0.8 times as long as propodi, proximal one-fifth of flexor margins unarmed, distal one-third only with slender subterminal spine closely appressed to unguis.

Description of holotype

Carapace. PCL 1.2 times width, dorsal surface slightly convex transversely; main transverse ridges mostly uninterrupted; ridges and striae with dense short setae and a few longer setae. Gastric region with 6 pairs of epigastric spines and 2 median spines. Cervical grooves distinct. Hepatic, parahepatic, anterobranchial and postcervical regions each with 1 small spine; lateral part of posterior branchial region with 8 transverse ridges including posterior submarginal ridge. Intestinal region without stria. Frontal margin transverse. Anterolateral spine reaching sinus between rostrum and supraocular spines, followed by 3 shorter spines on anterolateral margin. Branchial margins with 5 spines ( Figures 2 (e), 10(a,b)). Rostrum spiniform, 0.4 times as long as PCL, directed nearly horizontally in lateral view; lateral margins slightly crenulated distally; supraocular spines moderately long, slender, parallel in dorsal view, 0.4 times as long as rostrum ( Figures 2 (e), 10(a,b)). Pterygostomian flap with long and short transverse ridges, anterior margin terminating in 1 spinule ( Figure 10 (b)).

Sternum. Sternal plastron widest at sternite 7. Thoracic sternite 3 4.3 times as wide as long, half as wide as sternite 4; anterior margin granulate, with 2 lobes separated by wide V-shaped median notch. Sternite 4 with 2 pairs of oblique striae, anterior pair shorter than posterior pair, anterior margin widely contiguous to sternite 3. Sternite 5 with 1 short transverse stria anterolaterally and 1 short, longitudinal stria midlaterally; sternites 6 and 7 with 1 short transverse stria anterolaterally; each sternite with row of short setae on anterior ridge ( Figure 10 (e)).

Pleon. Smooth ( Figure 10 (d)), tergites 2–4 each with deep median transverse groove; tergite 2 with 1 lateral spine on each side of anterior ridge, 1 uninterrupted transverse stria anterior to, and 2 uninterrupted striae posterior to, transverse groove; tergite 3 with 2 uninterrupted transverse striae each anterior and posterior to transverse groove; tergite 4 with 2 uninterrupted transverse striae anterior to, and 1 medially interrupted stria posterior to, transverse groove. Tergite 5 with 4 uninterrupted transverse ridges, posterior ridge shortest. Tergite 6 with 2 squamiform ridges interrupted medially and laterally. Telson wider than long, longer squamiform ridges on anterior half ( Figure 10 (e)).

Eye. Eye moderately large; cornea dilated; maximum diameter 2.9 times distance between rostrum and supraocular spine, 0.4 times distance between anterolateral spines, 0.2 times PCL. Ocular peduncle with 1 stria on dorsal surface; eyelash long ( Figure 10 (a)).

Antennule. Antennular peduncle article 1 2.0 times as long as wide; reaching distal corneal margin; distal spines subequal in length; lateral margin with 2 spines, first lateral spine distinctly overreaching distal spines, second lateral spine very short, located anterior to midlength of article; ventral surface with a few scattered, short squamiform ridges ( Figure 10 (f)).

Antenna. Antennal peduncle reaching distal margin of cornea. Article 1 with distomesial spine reaching distal margin of article 3. Article 2 with distomesial spine overreaching distal margin of article 4, mesial margin armed with short spine; distolateral spine not reaching distal margin of article 3. Article 3 with minute distolateral spine. Article 4 unarmed ( Figure 10 (f)).

Mxp 3. Ischium 1.9 times as long as merus, disto-flexor and disto-extensor angles terminating in sharp spine. Merus flexor margin with 3 spines decreasing in size distally, extensor margin with distal spine. Carpus, propodus and dactylus unarmed ( Figure 10 (g)).

P1. Length 3.1 times PCL, surfaces with numerous squamiform ridges of various sizes bearing short setae. Ischium unarmed. Merus 4.1 times as long as wide; dorsal surface with irregular row 10 spines increasing in size distally; mesial margin with 3 spines increasing in size distally; ventral surface with 2 rows of spines, first row with 2 large spines under mesial row of spines, second row with 5 smaller spines; distal margin with 4 spines (dorsal, mesial, ventromesial and lateral spines; dorsomesial spine strongest, ventromesial spine smallest); lateral margin unarmed. Carpus 2.4 times as long as wide, 0.9 times as long as palm; dorsal surface with 1 row of 6 spines; mesial margin with 5 alternately large and small spines, flanked by dorsomesial row of 6 spines; lateral margin unarmed; ventral surface with 2 spines, ventrolateral distal angle produced in rounded lobe, armed with blunt spinule ( Figure 10 (h)). Palm 3.1 times as long as wide; dorsal surface with 2 rows of 5–6 small spines and 1 spine at dactylar articulation; ventral surface with 1 spine at dactylar articulation; dorsomesial margin with 5 large and 3 small spines; dorsolateral margin unarmed. Fingers subequal to palm length, terminating in sharp claws crossing distally; dorsal surfaces with scattered short setae; fixed finger with 1 row of 2 spines on dorsolateral surface, 2 subdistal spines on lateral margin, occlusal margin denticulate, with slightly larger teeth at regular intervals. Dactylus with short proximal spine, 2 subdistal spines on mesial margin, dorsomesial surface with 2 spines ( Figure 10 (i)).

P2–4. Compressed, lengths 2.1, 1.7 and 1.7 times PCL, respectively, surfaces squamate with iridescent setae on margins. Meri 0.8, 0.5 and 0.5 times as long as PCL, respectively, 6.4, 4.2 and 3.3 times as long as high, respectively; extensor margins with 9, 6 and 6 spines, respectively, distal spine longest; flexor margins with 3 spines on P2, 1 spine and 2 spinules on P3, 1 spine and 3 spinules on P4, distal spine longest. Carpi with 4, 3 and 3 spines on extensor margin, distal spine longest, flexor margin with 1 spine. Propodi 6.8, 5.0 and 5.4 times as long as wide, respectively, extensor margins unarmed, flexor margins with 11, 11 and 10 movable spines (including distal pair of spines), respectively. Dactyli 0.7, 0.8 and 0.8 times as long as propodi, respectively, flexor margins with 9, 8 and 7 movable spines, respectively, proximal one-fifth unarmed; distal one-third only with slender subterminal spine closely appressed to unguis ( Figure 10 (j–l, p)). P2 dactylus 4.2 times as long as wide.

Variation in paratypes

Carapace with 2 spines posterior to anterolateral spine in both paratypes. In the female paratype, tergite 2 with 1 (right) to 2 (left) spines on anterior ridge. In both paratypes, the antennal peduncle article 3 has a short, distinct distolateral spine. In the female paratype, P1 length 2.7 times PCL .

Distribution

Presently known only from Andaman Sea, 109–315 m depth ( Figure 1 ).

Remarks

Trapezionida aequispina sp. nov. shares the presence of spines only on lateral portions of the anterior ridge of the pleonal tergite 2, large corneas, 5 marginal branchial spines, antennular peduncle article 1 with subequal distal spines and the distomesial spine of antennal peduncle article 2 overreaching the article 4 with T. canopus Macpherson, Rodriguez-Flores and Machordom, 2020b , T. disiunctus Komai, 2011 and T. japonica Stimpson, 1858 from Japan. Additionally, T. aequispina sp. nov., T. canopus and T. japonica share the presence of 3 flexor spines and 1 disto-extensor spine on the merus of Mxp 3; T. aequispina sp. nov., T. canopus and T. disiunctus further share the presence of a spine-like seta appressed to unguis of P2–4 dactyli.

Nevertheless, the new species can be distinguished from the latter 3 species in the following characters:

(1) Carapace armed with 2 median epigastric spines and 1 hepatic spine (vs median epigastric spine absent in T. canopus ; hepatic spines absent in T. canopus and T. japonica );

(2) Thoracic sternite 4 with anterior margin widely contiguous to sternite 3 (vs sternite 4 with anterior margin contiguous along one-third of its length in T. japonica );

(3) Thoracic sternites 5–7 each with a few transverse striae (vs striae absent in T. disiunctus and T. japonica );

(4) Pleonal tergite 2 with 1 or 2 spines on each side of anterior ridge (vs anterior ridge unarmed in M. disiunctus ; 2 spines on each side in T. canopus and T. japonica );

(5) Mxp 3 merus with distinct disto-extensor spine (vs disto-extensor margin unarmed in T. disiunctus );

(6) P2–4 dactyli relatively shorter, broader (4.0 times as long as wide), with distinctly curved tips, flexor margins only with spine-like seta appressed to unguis along distal third (vs P2–4 dactyli relatively longer (> 5 times as long as wide), narrower, gently curved in T. canopus , T. disiunctus and T. japonica ; flexor margins unarmed along distal two-fifths in M. japonica ).

Figures

Figure 1. Map indicating collection sites of present specimens. 1, Gastroptychus valdiviae (Balss, 1913); 2, Grimothea krishaha sp. nov.; 3, Grimothea sp.; 4, Leptonida vigiliarum (Alcock, 1901); 5, Trapezionida aequispina sp. nov.; 6, Trapezionida bharuchai sp. nov.; 7, Leiogalathea sp.

Figure 2. Dorsal habitus. (a) Gastroptychus valdiviae (Balss, 1913). male, 6.0 mm PCL (IO/SS/ANO/ 00127); (b) Grimothea krishaha sp. nov. holotype, female, 3.5 mm PCL (IO/SS/ANO/00134); (c) Grimothea sp., female, 3.2 mm PCL (IO/SS/ANO/00143); (d) Leptonida vigiliarum (Alcock, 1901), male, 6.2 mm PCL (IO/SS/ANO/00133); (e) Trapezionida aequispina sp. nov. holotype, female, 7.0 mm PCL (IO/SS/ANO/00137); (f) Trapezionida bharuchai sp. nov. holotype, male, 4.7 mm PCL (IO/SS/ANO/ 00130); Leiogalathea sp., undetermined sex, 2.9 mm PCL (IO/SS/ANO/00126); (g) carapace, dorsal view; (h) P1, dorsal view. Scale bars: a, b, d–f, h = 2.0 mm; c, g = 1.0 mm.

Figure 3. Gastroptychus valdiviae (Balss,1913). Male, 6.0 mm PCL (IO/SS/ANO/00127).(a) Carapace and pleonal tergites 1–3, dorsal view; (b) carapace and pterygostomian flap, left lateral view; (c) thoracic sternites 3–5, ventral view; (d) pleonal tergite 6 and telson, dorsal view; (e) left antennal peduncle, dorsal view; (f) left Mxp 3, lateral view; (g) right P5 dactylus, lateral view; (h) right G1, dorsal view; (i) right G2, dorsal view. Scale bars: a, b = 2.0 mm; c, d, f = 1.0 mm; e, g–i = 0.5 mm.

Figure 10. Trapezionida aequispina sp. nov. (a–m, p) Holotype, female, 7.0 mm PCL (IO/SS/ANO/ 00137). (n–o) Paratype, male, 3.9 mm PCL (IO/SS/ANO/00138). (a) Carapace, dorsal view; (b) carapace and pterygostomian flap, left lateral view; (c) thoracic sternum, ventral view; (d) pleonal tergites 2–6, dorsal view; (e) telson, external view; (f) left antennular peduncle article 1 and antennal peduncle, ventral view; (g) left Mxp 3, lateral view; (h–i) left P1, dorsal view; (j) right P2, lateral view; (k) right P3, lateral view; (l) right P4, lateral view; (m) right P5 dactylus, lateral view; (n) right G1, dorsal view; (o) right G2, dorsal view; (p) right P4 dactylar tip, lateral view. Scale bars: a, b, d, h–l = 2.0 mm; c, e–g, o, p = 1.0 mm; m = 0.5 mm; n = 0.2 mm.